This invention relates to a shift detent assembly for a transmission, and more particularly, the invention relates to a shift detent to be used on manual transmission shift rails.
Manual transmissions are widely used in commercial trucks. Many transmission, engine, and driveline combinations, each of which may have several different lengths, are available to commercial truck consumers to meet their particular needs. As a result, the overall length of the driveline varies depending upon the particular combination.
A shift lever extends from the manual transmission into the vehicle cab and terminates with a knob in a location proximate the vehicle operator. The shift lever may be up to two to three feet in length. The driver moves a shift lever through a shift pattern. For balanced shift feel, the shift lever is configured so that it extends vertically from the shift lever pivot such that the center of gravity of the shift lever is over the shift lever""s pivot.
A detent assembly, which is in engagement with a transmission component, such as a shift rail, provides a shift feel to the vehicle operator during gear shifts and maintains the desired gears in engagement with one another. However, to accommodate the various powertrain combinations, the shift lever must be bent in such a manner to place the knob proximate to the vehicle operator. Vehicle vibrations acting at the center of gravity of the bent shift lever may cause an undesirable condition commonly known as xe2x80x9cjump outxe2x80x9d. Jump out occurs when the detent mechanism is unable to retain the shift rail in the selected position because of vibratory forces exerted by the shift lever on the shift rail. As a result, the selected gear becomes disengaged. A particular shift lever geometry may typically make the transmission susceptible to jump out in a particular direction. Therefore, what is needed is a detent assembly that prevents jump out in applications using a particular shift lever.
The present invention provides a detent assembly for a transmission including a transmission component, such as a shift rail, movable between a plurality of shift positions including first, second, and neutral shift positions. A contoured surface on the shift rail includes first and second recesses, respectively, corresponding to the first and second shift positions. A neutral recess is arranged between the first and second shift recesses corresponding to the neutral shift position. The first and second recesses, respectively, include first and second transition surfaces sloping towards the neutral recess with the second transition surface being steeper than the first transition surface. A detent assembly includes a biasing member and a detent member with the biasing member urging the detent member into engagement with the contoured surface. The biasing member generates a first force along the first transition surface and a second force along the second transition surface that increases at a greater rate than that of the first force. Said another way more work is required to move detent assembly out of the second recess than the first recess.
In this manner, a certain force versus rail displacement profile set may be generated to prevent jump out of first. Likewise, an opposite profile set may be generated to prevent jump out of second.
In addition to the symmetrical profile used for levers not prone to jump out, the above invention provides two shift rails with opposite, non-symmetrical profiles that can be used to prevent jump out with problematic shift levers.